Interleukin 10 inhibits interleukin 17 production by macrophages in mice with collagen-induced arthritis. (A) Macrophages in the joint tissues and synovial fluid (SF) taken from interleukin 10–knockout (IL-10−/−) mice and wild-type (WT) mice with collagen-induced arthritis (CIA) on day 45 after chicken type II collagen (CII) immunization were isolated. The total cellular RNA was extracted and analyzed for IL-17 mRNA by quantitative RT-PCR. Data are mean ± SEM (n = 3). *P < 0.05. (B) Macrophage proteins were extracted, and Western analysis was performed to detect protein levels of IL-17 and then quantified by densitometry. β-actin was used as an internal control. Data are mean ± SEM (n = 3). *P < 0.05. (C) Macrophages in the joint tissues and SF from IL-10−/− mice and WT mice with CIA on day 45 post–CII immunization were isolated, and cells were stained with fluorescein isothiocyanate–conjugated F4/80 (green) or Alexa Fluor 647–conjugated IL-17 (red) and analyzed by using confocal microscopy Bar = 25 μm. (D) In the joint synovium taken from IL-10−/− mice and WT mice with CIA, macrophages were detected by fluorescein isothiocyanate–conjugated F4/80 (green), Alexa Fluor 647–conjugated IL-17 (red) or immunofluorescence double-staining of frozen sections (original magnification, ×200). Boxed areas highlight IL-17/F4/80 double-positive macrophages in the joint synovium.